Superheterodyne receiver



July 27, 1937. M. J. o. STRUTT SUPERHETERODYNE RECEIVER Filed Dec. 19, 1934 INVENTOR l/AX/ll/ZMAA J. 0. JTWTT BY gMM/ ATTORNEY Patented July 27, 1937 are sure SUPERHETERODYNE RECEIVER Application December 19, 1934, Serial No. 758,224 In Germany February 12, 1934 Claims.

This invention relates to a superheterodyne receiving arrangement in whichv a tube having a plurality of grids is used as a first detector and, if desired, also as agenerator for the oscillations to be locally produced.

An object of the invention is to provide a vacuum tube arrangement in which the tube has a control grid on. which the signal oscillations are impressed, at second grid onwhich a local oscillation frequency is impressed and a shielding grid between the grids which serves to prevent the oscillator frequency from being fed back into the signal circuit.

A further object is to provide a tube having a plurality of grids which functions to amplify the incoming signal energy and combine it with the energy of a local oscillator to produce a beat or intermediate frequency energy, one of the grid circuits of the device being made resonant to the intermediate frequency. Also, if desired, the local oscillation frequency may be supplied to the latter grid circuit through the circuit tuned to the in: termediate frequency.

Other objects of the invention will become apparent to; those skilled in the art as the description thereof proceeds in connection with the accompanying drawing, in which;

Figs. 1 to 4 are schematic circuit diagrams of rectifying arrangements embodying the invention.

An arrangement of this type is represented in Fig. 1 of the. accompanying drawing, wherein the tube it which has a plurality of grids serves as a first detector tube and as a generator for the oscillations to be locally produced.

In the arrangement shown in Fig. 1 the received oscillations are supplied to the grid l of the tube H], the grid having a negative bias which may be produced by a battery 20 or other known means. The control grid circuit 2| is preferably tunable to the incoming signal frequency as by the variable condenser 22. The tension of the grids 2 and 3 is positive with respect to the oathode M. The grid 2 serves as a screen and an oscillatory circuit 52 is interposed between the grid 3 and the cathode ll. Since the grid 4 has a negative bias, a negative resistance will occur between the grid 3 and the cathode II so that oscillations, whose frequency depends on the tuning of this circuit are produced in the circuit l2 tunable by condenser 23.

Since, as is well known, the anode current depends on the product of the voltages set up at the grids l and 3, oscillations whose frequency is determined by the sum and difference frequency of the received and of the locally produced oscillations will occur in the circuit 13 of the anode circuit of the tube It. This rectifying method is more generally known as multiplication rectifying.

By means of the arrangement referred to a conversion slope of about 0.5 ma./v. is ensured.

The present invention has for its purpose to provide an arrangement by means of which a conversion slope can be achieved which is at least to times greater than that ensured by means of the known arrangements.

In the arrangement according to the invention, in which the received and the locally produced oscillations are each supplied to a different grid of the rectifying tube, a circuit tuned to the difference frequency is interposed in the conductor leading to a third grid on which grid the locally produced oscillations and the received oscillations assemble.

The invention will be more clearly understood by reference to the accompanying drawing in which Figures 2 and 3 represent different embodiments.

In the arrangement shown in Fig. 2 the received oscillations are supplied to the grid l, as is also the case in known arrangements. Also in this case the voltage at the grid 3 is positive and that of the grid 4 is negative, due to which a negative resistance occurs between the grid 3 and the cathode I l, and oscillations are generated in the circuit H2. The grid 2 serves as a screen for avoidingradiation of the local oscillations produced in the circuit [2.

The output circuit of the tube It comprises an oscillatory circuit [3 which is tuned to the desired intermediate frequency. According to the invention an oscillatory circuit M including coil 24 and condenser 25 which is tuned to the desired intermediate frequency is inserted in the arrangement set out above in the circuit connecting the grid 3 to the grid 4 and which includes a condenser 26. Through said circuit M the local oscillations occurring in the circuit l2 are supplied to the grid 4. The oscillations received at the grid 5 will occur in an amplified manner in the circuit 12 and are also impressed on the grid 4 through the circuit [4. A resistor 21 may be connected as shown.

In the arrangement referred to above, the received and the locally produced oscillations are rectified according to the rectifying method, which is more generally known as grid rectification, in which the circuit M serves as a grid condenser.

Fig. 3 shows an arrangement similar to that of Fig. 2 and in which a screen grid 5 is provided between the grid 4 and the anode 9, said grid serving for avoiding back-coupling between the output circuit i3 and the oscillatory circuit M both of which are tuned to the same intermediate frequency.

In the arrangement shown in Fig. 4 the grids I and 2 that are nearest the cathode ii are used as a grid and as an anode respectively of a generator for producing the local oscillations. The oscillatory circuit E5 in which the local oscillations occur, lies between the first grid and the cathode and includes a coil 28 coupled with a coil IS in the circuit of the second grid, which functions as an anode of the local generator. In this arrangement the signal or received oscillations are supplied to the fourth grid. A screen grid 3 lies between the auxiliary anode 2 and the grid 4. However, it is also possible to design the auxiliary anode 2 in such a manner that it serves at the same time as an anode and as a screen grid. The voltage at the grid 5 is positive and between the cathode and this grid lies an oscillatory circuit l2, in which both the received oscillations and the locally generated oscillations occur in an amplified manner. Through a circuit M tuned to the desired intermediate frequency the received oscillations and the locally generated oscillations are supplied to the grid 6 which has a negative voltage. The anode circuit comprises again a circuit l3 which is tuned to the desired intermediate frequency and wherein the rectified oscillations occur. As in Fig. 3 a screen grid 1 may be interposed between the grid 6 and the anode 9, said screening grid neutralizing the back coupling between the circuits l3 and M.

The last mentioned arrangement has the advantage over the first mentioned one that the amplitude of the oscillations occurring in the output circuit can be controlled by controlling the bias of the grid 4, as by varying the voltage of battery 20 without affecting the slope of the tube and consequently the working of the generator.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a detecting arrangement the combination of a vacuum tube having a plurality of grids, a cathode and a plate, a circuit tunable to the signal frequency connected between one of said grids and said cathode, a circuit tunable to a frequency different from the signal frequency by a desired beat frequency connected to a second grid, means for impressing a potential which is positive with reference to that of said cathode on said second grid, a circuit tuned to the beat frequency connected to a third grid, means for applying a steady negative potential to said third grid and an output circuit connected to said plate and including means for impressing a potential which is positive with reference to that of said cathode on said plate.

2. In a superheterodyne receiver, the combination of an electron discharge tube having a cathode, an anode and a signal control grid, means for impressing signal frequency variations on said grid, an oscillator grid, a circuit tunable to the local oscillation frequency connected to said oscillator grid, means for impressing a potential which is positive with reference to that of said cathode on said oscillator grid, a third grid located between said anode and oscillator grids, a circuit tuned to the intermediate frequency connected to said third grid, means for impressing a potential which is negative with reference to that'of said cathode on said third grid, means for impressing a positive potential on said anode and a condenser having one side connected to the end of said last named circuit of low alternating current potential and its other side connected to said oscillator grid.

3. In a superheterodyne receiver, the combination of a vacuum tube having a cathode, an oscillator grid, a signal control grid, third and fourth grids and an anode, a circuit tuned to a local oscillation frequency connected between said cathode and oscillator grid and including means for impressing a potential which is positive with reference to that of said cathode on said oscillator grid, a circuit tunable to an incoming signal frequency connected between said cathode and signal control grid and including a source of negative bias potential, a circuit tuned to the intermediate beat frequency connected to said third gridand including means for impressing a potential which is positive with reference to that of said cathode on said third grid, a circuit having a portion tuned to the intermediate beat frequency connected to said fourth grid and including means for impressing a potential which is negative with reference to that of said cathode on said fourth grid, a path having capacitive reactance connecting said last named circuits and an output circuit including a source of positive potential connected to said anode.

4. The combination defined in the preceding claim in which a screen grid is located between said fourth grid and said anode and an additional screen grid is located between said signal control grid and said oscillator grid and means for maintaining said screen grids at a positive potential with reference to said cathode.

5. In a superheterodyne receiver, the combination of an electron discharge tube having a cathode, an anode and a signal control grid, an oscillator grid and a third grid arranged between said cathode and anode in the order named,

an input circuit responsive to incoming signal variations connected between said signal control grid and cathode, a circuit including a portion tuned to a local oscillation frequency connected to said oscillator grid, a source of positive potential connected to said last named circuit and to said oscillator grid, means for impressing a voltage which is negative with reference to said cathode on said third grid whereby a negative transconductance with reference to the current to said oscillator grid results, an output circuit tuned to the intermediate frequency connected to said anode and means for impressing a potential on said anode which is positive with reference to that of said cathode.

MAXIMILIAAN JULIUS OTTO STRUTT. 

